Expulsion tank constructions of the non-spherical variety feature a tank shell having first and second ends and a generally cylindrical side wall for joining such ends; a bladder fixed within the tank shell and cooperating therewith to define product storage and expulsion fluid chambers; and expulsion fluid inlet/outlet means carried by the tank shell in flow communication with the product storage and expulsion fluid chambers, respectively. Bladders used in such tanks may be variously defined, as by metal bellows, rolling metal diaphragms, and by rubber or plastic expansible and/or collapsible bladders.
Heretofore, when employing a bladder in the form of a metal bellows, the product is commonly disposed within the bellows and expelled from the tank incident to an axially directed compression or collapse of the bellows, in the manner shown for instance in U.S. Pat. No. 3,296,803 to Kroekel.
U.S. Pat. No. 3,469,502 to Gardner is of interest for its disclosure of the operational characteristics of a conventional bellows and particularly for its discussion of factors establishing the limiting modes of extreme compression and extreme extension of bellows designs featuring different convolution side wall configurations. The curved convolution side wall configuration to which the Gardner patent is directed has been used commercially in expulsion tank structures of the general type described in the above mentioned Kroekel patent, due to the relatively large deflection ratio obtainable therewith, as compared to prior bellows side wall configurations.
Thus, in prior applications of a Gardner bellows in a positive expulsion tank, such bellows has functioned in a compressive mode, during the product expulsion operation. The limiting mode of extreme extension would correspond to the product cavity full condition, wherein the convolution side walls preferably retain some degree of curvature in order to accommodate for temperature induced expansion/contraction of the stored product. The limiting mode of extreme compression would correspond to the product cavity empty condition, wherein the convolution side walls preferably nest in surface to surface engagement in order to expel all products from within the confines of the convolutions.
Recognizing the deflection limitations placed upon a collapsing bellows by its limiting modes of expansion and compression, and resultant modest product storage capabilities, tests have been conducted using a Gardner type bellows to effect product expulsion incident to expansion of the bellows to and beyond its limiting mode of extreme extension. It was found that extensions beyond the limiting mode of extension result in buckling failure of the bellows accompanied by a marked increase in the pressure required to extend the bellows beyond this point. Tearing of the bellows material incident to serious buckling of the crest portions of the convolutions coupled with substantial increases in required expulsion pressure have heretofore placed a definite limitation on the utilization of an expanding bellows in a positive expulsion tank.
In addition to the above discussed Kroekel and Gardner patents, U.S. Pat. No. 2,798,639 to Urban and U.S. Pat. No. 3,847,309 to Grossman are cited as being of possible interest to the state of the art relating to the present invention.
The Grossman patent is representative of numerous prior patents disclosing expulsion tanks utilizing a rolling metal type diaphragm; this patent being specifically mentioned for its showing of the utilization of rings to reinforce the cylindrical wall of a rolling diaphragm and strengthen same against buckling pressure of a pressurizing medium. The buckling phenomena characteristic of a rolling diaphragm type expulsion bladder is not related directly to the buckling phenomena characteristic of a bellows type bladder, in that with the latter buckling limits of extreme compression or extension are independent of the pressure of the expulsion fluid effecting operations of the bellows intermediate these extremes.
U.S. Pat. No. 2,798,639 is believed representative of numerous patents suggesting reinforcement of crests and/or root portions of a bellows when such bellows is fabricated from a pliable, non-metallic material, including for instance cloth, rubber and plastic, in order to rigidify the convolutions and prevent deformation thereof under normal bellows operating conditions, due to the necessary pressure differential existing across the bellows walls. In a metallic bellows of the type intended for use in an expulsion tank, the rigidity or structural strength of the convolutions of the bellows is sufficient to prevent radially directed expansion or collapse of the convolution, due to pressure differentials existing across the bellows walls.